The present invention relates to the insulation film used between semiconductor device layers, and the low dielectric constant material having thermal resistance of a semiconductor device, which is applicable for electric circuit appliances.
Along with improvement in speed and high integration of a semiconductor device, the problem of signal retardation has become serious. The signal retardation is expressed with the product of resistance R of a wire and capacity C between wires and between layers. In order to suppress the retardation to the minimum, it is an effective means to lower the dielectric constant of an insulation film between layers, as well as to lower resistance of wiring.
Recently, in order to lower the dielectric constant of an insulation film between layers, there is proposed a method for forming an insulation film between layers using a silicon oxide film (SiOF film) wherein the fluorine atom is incorporated. Moreover, since an organic compound material can relatively lower dielectric constant, there is proposed a method for forming an insulation film between layers by using a parylene deposit film or a polyimide film wherein a fluorine atom is incorporated (Hideki Shibata, Densijyouhoutsuusin Gakkaishi Vol.80, No.3 p235(1997)).
By the way, the dielectric constant of the insulation film between layers becomes lower than that of the conventional film, when the insulation film between layers is formed by the above SiOF film. However, a dielectric constant thereof becomes about 3.2 to 3.5, capacity between wires can not be reduced and signal propagation de of wires can not be sufficiently prevented.
Moreover, the dielectric constant 2.7 is attained by using the film wherein the fluorine atom is incorporated into the polyimide and aryl ether polymer, when an insulation film between layers is formed with the organic compound material mentioned below. But it is not still sufficient. By using deposit film of parylene dielectric constant 2.4 can be attained, but the process for preparing a semiconductor device is limited, since thermal resistance is only about 200 to 300xc2x0 C.
The dielectric constant of 2.0 to 2.5 has been reported in porous SiO2 film. But there is a problem that mechanical strength (CMP polishing process resistance) is low due to high porosity, and a pore diameter varies.
Since thermal conductivity of these polymeric materials and porous SiO2 film is lower than that of the conventional insulation film between layers of SiO2, there is a problem that the wiring life is degraded (electromigration) by the wire temperature rise.
As mentioned above, the insulation film between layers has been desired, which has low dielectric constant and is excellent in thermal resistance, mechanical strength, and the thermal conductivity. Concretely, in design-rule 0.13 to 0.10 xcexcm, the film is required, which has mechanical strength and thermal conductivity not less than an SiO2 film, dielectric constant of at most 2.4, and thermal resistance (thermal decomposition temperature) of at least 450xc2x0 C.
The object of the present invention is to provide the low dielectric constant film having thermal resistance, which is excellent in thermal resistance, has low dielectric constant and can be applied to appliances of semiconductor device and electric circuit, and the process for forming the same.
The low dielectric constant film having thermal resistance of the present invention comprises molecules comprising boron, nitrogen, and hydrogen, wherein the number of nitrogen atom is 0.7 to 1.3 and the number of hydrogen atom is 1.0 to 2.2 based on one boron atom, and of which dielectric constant is at most 2.4.
The low dielectric constant film having thermal resistance of the present invention has thermal decomposition temperature of at least 450xc2x0 C. in the above low dielectric constant film having thermal resistance.
The process for forming the low dielectric constant film having thermal resistance of the present invention is the process wherein the process for forming the low dielectric constant film having thermal resistance on the substrate surface is the process for forming the low dielectric constant film having thermal resistance according to chemical vapor deposition.
The process for forming the low dielectric constant film having thermal resistance of the present invention is the process wherein gas containing diborane and gas containing annonia are used as raw gas in the chemical vapor deposition in the process for forming the low dielectric constant film having thermal resistance.
The process for forming the low dielectric constant film having thermal resistance of the present invention is the process wherein gas containing diborane is used as raw gas in the chemical vapor deposition in the process for forming the low dielectric constant film having thermal resistance.
The insulation film between semiconductor layers of the present invention is the insulation film between semiconductor layers comprising the low dielectric constant film having thermal resistance.
The insulation film between semiconductor layers of the present invention is the insulation film between semiconductor layers obtained by the process for forming the low dielectric constant film having thermal resistance.
The semiconductor device of the present invention is the semiconductor device comprising the insulation film between semiconductor layers.
Example of the compound in the film of the present invention comprising molecules comprising boron, nitrogen and hydrogen, wherein the number of nitrogen atom is 0.7 to 1.3 and the number of hydrogen atom is 1.0 to 2.2 based on one atom of boron, is concretely borazine shown in the following formula (1) (which is called as inorganic benzene or borazol). 
The compounds obtained by molecular propagation of the structure shown in the above formula (1) and the derivative structure as thereof as a basic unit are suitable for the low dielectric constant film having thermal resistance of the present invention. The low dielectric constant film having thermal resistance comprising the compounds can be applied for the insulation film between semiconductor layers, and by using the insulation film the excellent semiconductor device can be prepared.
The reasons why the material (or compound) of the present invention can lower the dielectric constant and achieve dielectric constant of at most 2.4 are follows.
That is, the dielectric constant xcex5 is generally described with sum of polarization such as electron polarization, atom polarization, orientation polarization, and interface polarization. But it is sufficient to consider only the electron polarization and the atom polarization as polarization controlling dielectric constant, as long as there is no contribution of interfacial polarization in the high frequency region of at least 1 MHz in the present invention and there is used the material showing no orientation. The present invention is completed by results of molecular design for searching the material with the small polarizability of both electron polarization and atomic polarization.
If molecular polarizability a is defined as
xcex1=xcex1 (electron polarization)+xcex1 (atom polarization)
dipole-moment xcexc of a molecule is given as a function of an electric field E and basic coordinate q of a molecule. The electron polarization and the atom polarization can be evaluated by differentiating the dipole moment xcexc with the electric field E.
dxcexc(E,q)/dE=xcex4xcexc(E,q)/xcex4Excex4xcexc (E,q)/xcex4qxcex4xcexc/xcex4E
xcex1(electron polarization)=xcex4xcexc(E,q)/xcex4E
                              α          ⁢                      xe2x80x83                    ⁢                      (                          atom              ⁢                              xe2x80x83                            ⁢              polarization                        )                          =                  δ          ⁢                      xe2x80x83                    ⁢                                    μ              ⁡                              (                                  E                  ,                  q                                )                                      /            δ                    ⁢                      xe2x80x83                    ⁢          q          ⁢                      xe2x80x83                    ⁢                      δμ            /            δ                    ⁢                      xe2x80x83                    ⁢          E                                        =                  δ          ⁢                      xe2x80x83                    ⁢                      μ            /            δ                    ⁢                      xe2x80x83                    ⁢                                    q              ⁡                              (                                                      δ                    2                                    ⁢                                      E                    /                    δ                                    ⁢                                      xe2x80x83                                    ⁢                  q                  ⁢                                      xe2x80x83                                    ⁢                  δ                  ⁢                                      xe2x80x83                                    ⁢                  q                                )                                                    -              1                                ⁢          δ          ⁢                      xe2x80x83                    ⁢                      μ            /            δ                    ⁢                      xe2x80x83                    ⁢          q                                        =                  δ          ⁢                      xe2x80x83                    ⁢                      μ            /            δ                    ⁢                      xe2x80x83                    ⁢                                    q              ⁡                              (                κ                )                                                    -              1                                ⁢          δ          ⁢                      xe2x80x83                    ⁢                      μ            /            δ                    ⁢                      xe2x80x83                    ⁢          q                    
As shown above, the atom polarization is in inverse proportion to bonding strength xcexa (force constant) between atoms.
Next, concrete calculation method of the polarizability a is explained as follows. Dielectric constant xcex5 of fluorinated parylene is 2.4 as mentioned above, and molecular orbital calculation was carried out in the model compounds shown in the following formula (2) to (7). Table 1 collectively shows the results of calculation. 
As is clear from Table 1, it is found out that molecular polarizability a in the borazine system (formula (5), (6) and (7)) is smaller than that in the hydrocarbon system (formula (2), (3) and (4)). Namely, the borazine system theoretically shows a small dielectric constant. The molecular polarizability ratios of each system are as follows, respectively.
Formula (5) Formula (2)=0.85
Formula (6) Formula (3)=0.88
Formula (7) Formula (4)=0.86
It shows that it is predicted that dielectric constant xcex5 of the borazine system (formula (7)) is 2.0 to 2.1, since the dielectric constant F of fluorinated parylene (formula (4)) is 2.4.
From the calculation results, the compound containing borazine skeleton molecule in its molecule can make dielectric constant at most 2.4. Concrete examples are the compounds satisfying that the number of nitrogen atom is 0.7 to 1.3 and the number of hydrogen atom is 1.0 to 2.2 based on one atom of boron, in the film comprising the molecules comprising boron, nitrogen, and hydrogen. The number of nitrogen is preferably 0.8 to 1.1, and the number of hydrogen atom is preferably 1.0 to 1.5. If the number of nitrogen atom is out of the range, an amount of the borazine skeleton becomes too small in the molecule, dielectric constant becomes large to above 2.4. If the number of hydrogen atom is out of the range, an amount of the borazine skeleton becomes too small in the molecule, dielectric constant xcex5 becomes large to above 2.4 due to graphitization. The dielectric constant is preferably at most 2.2. If the dielectric constant is more than 2.4, signal tends to be delayed in the semiconductor device.
Therefore, concrete examples of the present invention are the materials containing the structure shown in the following formula (8) to (12) in its molecule 
The present invention can improve thermal resistance, since the inorganic polymer material is used, which is excellent in thermal resistance compared with the organic polymer material.
The low dielectric constant film having thermal resistance of the present invention comprising boron, nitrogen, and hydrogen can be prepared by the method described in, for example, S. V. Nguyen, T. Nguyen, H. Treichel, 0. Spindler, J.Electrochem.Soc., Vol.141, No.6, pl633(1994), W. F. Kane, S. A. Cohen, J. P. Hummel, B. Luther, J.Electrochem.Soc., Vol.144, No.2, p658(1997), M. Maeda, T. Makino, Japanese Journal of Applied Physics, Vol.26, No.5, p660(1987), and the like. Namely, the film can be obtained according to a condensation reaction with chemical vapor deposition (CVD method) by using diborane (B2H6) and ammonia (NH3), or borazine (B3N3H6) and nitrogen(N2) as a raw material. The thickness of the film is preferably 0.3 to 0.8 xcexcm.
Gas containing diborane and gas containing ammonia are preferably used as the raw gas from the viewpoint of gas vapor pressure suitable for CVD and condensation reactivity. Gas containing borazine is more preferably used as the raw gas from the viewpoint of the amount of a borazine skeleton structure after condensation reaction by CVD.
In the above synthesis inert gas such as argon (Ar) may be used as carrier gas of the material.
A conventional plasma CVD device may be used as a device for chemical vapor deposition (CVD) used in the present invention.
In addition, the polymer is excellent in thermal stability, although it is necessary to handle borazine carefully since borazine may be ignited spontaneously in air.
The thermal decomposition temperature of the low dielectric constant film having thermal resistance is preferably at least 450xc2x0 C., more preferably at least 480xc2x0 C. If the temperature is less than 450xc2x0 C., there is a tendency that the thin film becomes bad at heating in the preparation process for a semiconductor device.
The low dielectric constant film having thermal resistance can be used for the low dielectric constant film having thermal resistance as it is, but the formed film may be annealed at not more than 800xc2x0 C. (temperature in which graphitization is not largely carried out).
The low dielectric constant film having thermal resistance of the present invention can be applied to various electric appliances such as an insulation film between layers for LSI device and IC substrate.